T helper type 2 development can be influenced by such cytokines as IL-33 and thymic stromal lymphopoietin,54,55 but IL-4 remains the primary signal that drives Th2 commitment from naive precursors.55,56 The Th2 differentiation involves the integration of signals both from

the T-cell receptor and from IL-4 signalling via STAT6, which culminates in the induction of the GATA3 transcription factor. GATA3 subsequently promotes transcription at the Th2 cytokine locus containing the IL-4, IL-5 and IL-13 Stem Cell Compound Library clinical trial genes. This pathway also acts acutely to inhibit expression of the IL-12Rβ2 subunit.57 Consequently, induction of GATA3 serves to block Th1 development while positively regulating Th2 commitment. Moreover, while there seems to be some level

of plasticity in Th2 cells,58 GATA3 is involved in an autoregulatory feedback loop check details that maintains Th2 commitment even in the absence of further IL-4 signalling.59,60 Hence, autoregulation by GATA3 represents an important stabilizing mechanism for Th2 commitment. However, early reports demonstrated that IFN-α/β could inhibit IL-5 secretion and eosinophil migration during allergic responses.61,62 Furthermore, IFN-α/β treatment of bulk CD4+ T cells during acute stimulation seemed to inhibit IL-5, but not IL-4 or IL-13. This was somewhat curious considering the dominant role played by IL-4 and GATA3 in Th2 effector function. Yet, despite these and other similar studies, one central question remained: can IFN-α/β regulate the ability of IL-4 to drive Th2 differentiation? Recently, Huber et al.63 found that unlike the Th1-promoting cytokines IL-12 and IFN-γ, IFN-α/β potently and specifically inhibited the ability of IL-4 to drive Th2 differentiation of human cells but not murine cells. Moreover, IFN-α/β destabilized pre-committed Th2 cells and blocked Th2 cytokine expression. Interferon-α/β also reduced expression of the Th2 marker, CRTH2. It appears to do this, at least in part, by suppressing mRNA and protein levels of GATA3, Amisulpride which is critical for expression of CRTH2 as well as Th2-associated cytokines. While the underlying mechanism of GATA3 suppression is not yet clear, there are a few clues. First, as neither IL-12 nor

IFN-γ inhibits Th2 commitment, the effect is not likely to be mediated by STAT4 or STAT1. Furthermore, the inhibition of Th2 cells by IFN-α/β paralleled recent studies demonstrating that type-III interferon (IFN-λ) can also suppress Th2 responses.64 Since both IFN-α/β and IFN-λ activate STAT2 and drive ISGF3 complex formation,65 STAT2 may play a crucial role in suppressing human Th2 development. In addition to Th2 cells, there is increasing evidence that Th17 cells contribute to a variety of inflammatory processes involved in autoimmunity and allergic diseases.66 The Th17 cells are regulated by combined signalling via transforming growth factor-β, IL-6, IL-23 and IL-1β, culminating in the induction of the transcription factor retinoic acid-related orphan receptor γT.